Field of the Invention
Embodiments of the present invention relate generally to a multi charged particle beam exposure method, and a multi charged particle beam blanking apparatus, and more specifically, relate to a beam irradiation method in multi-beam writing, for example.
Description of Related Art
The lithography technique that advances miniaturization of semiconductor devices is extremely important as a unique process whereby patterns are formed in semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required for semiconductor device circuits becomes progressively narrower year by year. The electron beam writing technique, which intrinsically has excellent resolution, is used for writing or “drawing” with electron beams on a wafer, etc.
As a known example of employing the electron beam writing technique, there is a writing apparatus using multi-beams. Since it is possible for multi-beam writing to irradiate multiple beams at a time, the writing throughput can be greatly increased in comparison with single beam writing. For example, a writing apparatus employing the multi-beam technique forms multi-beams by letting portions of an electron beam emitted from an electron gun pass through a corresponding hole of a plurality of holes in a mask, performs blanking control for each beam, reduces each unblocked beam by an optical system, and deflects the beam by a deflector to irradiate a desired position on a target object or “sample”.
In multi-beam writing, the dose of each beam is individually controlled based on the irradiation time. A control circuit for performing an individual control is included in a blanking aperture array apparatus mounted in the body of the writing apparatus. In multi-beam writing, for further improving the throughput, it would be necessary to increase the current density so as to reduce the irradiation time of each beam. However, when increasing the current density, there is a problem in that a so-called blur and/or positional deviation of a multi-beam image occurs due to the Coulomb effect, depending on a total current amount of simultaneously irradiating multi-beams.
As for the apparatus which performs ON/OFF control of beam arrays at the same timing, there is proposed a method of grouping beam arrays, and applying a blanking voltage (signal) from the blanking control circuit outside the writing apparatus to the blanker array in each group, at a different (shifted) applying time to the apparatus in order to shift the irradiation timing of beams (for example, refer to Japanese Patent Application Laid-open No. 2007-329220). Moreover, it is also proposed that by this method the dose can be adjusted for each group. However, according to this method, it is difficult to individually control the dose of each beam by the irradiation time. Further, it is also difficult to include a control circuit for controlling the dose of an individual beam in the blanking aperture array apparatus.
Then, it can be thought to group beam arrays, and, to transmit, for each group, an exposure time control signal at a different (shifted) time to a blanking aperture array apparatus including a control circuit for controlling the dose of an individual beam in order to shift the irradiation timing of beams. However, according to this method, since the cycle of one beam shot is merely divided into cycles of two beam shots, the number of times of transmitting the exposure time control signal becomes double, and, as a result, the exposure time becomes double. Therefore, even if intending to improve the throughput by performing multi-beams, it turns out to be difficult to thoroughly achieve the effect.